Quantification of Myocardial Perfusion Reserve Using Dynamic SPECT Imaging in Humans: A Feasibility Study

Abstract

Myocardial perfusion imaging (MPI) is well established in the diagnosis and workup of patients with known or suspected coronary artery disease (CAD); however, it can underestimate the extent of obstructive CAD. Quantification of myocardial perfusion reserve with PET can assist in the diagnosis of multivessel CAD. We evaluated the feasibility of dynamic tomographic SPECT imaging and quantification of a retention index to describe global and regional myocardial perfusion reserve using a dedicated solid-state cardiac camera. Methods Ninety-five consecutive patients (64 men and 31 women; median age, 67 y) underwent dynamic SPECT imaging with 99mTc-sestamibi at rest and at peak vasodilator stress, followed by standard gated MPI. The dynamic images were reconstructed into 60–70 frames, 3–6 s/frame, using ordered-subsets expectation maximization with 4 iterations and 32 subsets. Factor analysis was used to estimate blood-pool time–activity curves, used as input functions in a 2-compartment kinetic model. K1 values (99mTc-sestamibi uptake) were calculated for the stress and rest images, and K2 values (99mTc-sestamibi washout) were set to zero. Myocardial perfusion reserve (MPR) index was calculated as the ratio of the stress and rest K1 values. Standard MPI was evaluated semiquantitatively, and total perfusion deficit (TPD) of at least 5% was defined as abnormal. Results Global MPR index was higher in patients with normal MPI (n = 51) than in patients with abnormal MPI (1.61 [interquartile range (IQR), 1.33–2.03] vs. 1.27 [IQR, 1.12–1.61], P = 0.0002). By multivariable regression analysis, global MPR index was associated with global stress TPD, age, and smoking. Regional MPR index was associated with the same variables and with regional stress TPD. Sixteen patients undergoing invasive coronary angiography had 20 vessels with stenosis of at least 50%. The MPR index was 1.11 (IQR, 1.01–1.21) versus 1.30 (IQR, 1.12–1.67) in territories supplied by obstructed and nonobstructed arteries, respectively (P = 0.02). MPR index showed a stepwise reduction with increasing extent of obstructive CAD (P = 0.02). Conclusion Dynamic tomographic imaging and quantification of a retention index describing global and regional perfusion reserve are feasible using a solid-state camera. Preliminary results show that the MPR index is lower in patients with perfusion defects and in regions supplied by obstructed coronary arteries. Further studies are needed to establish the clinical role of this technique as an aid to semiquantitative analysis of MPI.

Dynamic Single-Photon Emission Computed Tomography Data Analysis: Capabilities for Determining Functional Significance of Coronary Artery Atherosclerosis

“…It is caused by linear dependence of [ 15 O]H 2 O extraction fraction on myocardial flow rate as well as by higher resolution power of positron emission tomography scanners. Data obtained in our study agree with the results of other research groups who showed principal feasibility of myocardial flow reserve assessment by the methods of dynamic SPECT [4,6,7] or planar scintigraphy [2] with high diagnostic accuracy values.…”

“…Literature describes this phenomenon by term "balanced ischemia" where a uniform decrease in an indicator accumulation is observed over the entire left ventricular (LV) myocardium [5,6]. One of the ways to diagnose balanced ischemia of the myocardium in multivessel coronary artery disease consists in an assessment of myocardial flow reserve [7,8].…”

Moving ahead with CZT technology

“…The introduction of semiconductor detector technology using synthetic crystals composed of CZT undeniably constituted a revolutionary milestone in technical innovation for nuclear MPI, offering a variety of interesting new possibilities ranging from dynamic SPECT imaging for non-invasive quantitation of myocardial blood flow, 8 over respiratory triggering, 9 to low isotope dose SPECT with significantly reduced ionizing radiation exposure. 10 However, particularly the strive for a further reduction in radiation dose exposure will in turn inevitably again lead to a future increase in acquisition times because with the current CZT system sensitivity very short acquisition times of only 2 or 3 min may not yield sufficient count statistics if the isotope dose is substantially reduced.…”

PET should not replace routine SPECT MPS for the assessment of patients with known or suspected CAD

“…17 The problem caused by qualitative imaging is uncertain. Non-regional markers of ischemia such as hemodynamic and ECG changes, post-stress LV stunning, transient RV prominence, and lung activity often flag when qualitative SPECT may be underestimating ischemia.…”